Heretofore, ring field illumination systems used in microlithography used a curved mercury capillary lamp cooled with compressed air. While such systems have met with success, the system of the present invention is characterized by one or more of the following features: more efficient, brighter, less vibration, and constant light output rather than the time varying output characteristic of an alternating current source.
One of the main goals in the design of condenser systems is to achieve as high an intrinsic brightness in the image as possible with minimum electrical power input. In general, short arcs and capillary arcs have about equal electricity to light conversion factors, but the short arc has a much higher intrinsic brightness because all the power is radiated from a very small volume. By using an elliptical reflector as much as 80% of the light from a short arc can be imaged into a 3 mm. diameter spot. This invention permits the small unevenly illuminated image of the arc from a short arc lamp to be transformed into an evenly illuminated arcuate shaped source of illumination from which an efficient and uniform illumination system for a ring field projection system can be fashioned.